Variable star

variablevariable starsvariability
Cyclotron radiation beamed from the accretion region can cause orbital variations of several magnitudes. These symbiotic binary systems are composed of a red giant and a hot blue star enveloped in a cloud of gas and dust. They undergo nova-like outbursts with amplitudes of up to 4 magnitudes. The prototype for this class is Z Andromedae. AM CVn variables are symbiotic binaries where a white dwarf is accreting helium-rich material from either another white dwarf, a helium star, or an evolved main-sequence star. They undergo complex variations, or at times no variations, with ultrashort periods. There are two main groups of extrinsic variables: rotating stars and eclipsing stars.

Messier 81

M81Bode's Galaxy3031
Messier 81 (also known as NGC 3031 or Bode's Galaxy) is a spiral galaxy about 12 million light-years away, with a diameter of 90,000 light years, about half the size of the Milky Way, in the constellation Ursa Major. Due to its proximity to Earth, large size, and active galactic nucleus (which harbors a 70 million supermassive black hole), Messier 81 has been studied extensively by professional astronomers. The galaxy's large size and relatively high brightness also makes it a popular target for amateur astronomers. Messier 81 was first discovered by Johann Elert Bode on 31 December 1774. Consequently, the galaxy is sometimes referred to as "Bode's Galaxy".

Light curve

lightcurvelight-curvelight curves
For example, PA-99-N2 is a microlensing event that may have been due to a star in the Andromeda Galaxy that has an exoplanet. U = 0 → Result later proven incorrect. U = 1 → Result based on fragmentary light curve(s), may be completely wrong. U = 2 → Result based on less than full coverage. Period may be wrong by 30 percent or ambiguous. U = 3 → Secure result within the precision given. No ambiguity. U = n.a. → Not available.

Messier 41

M412287NGC 2287
M41 lies about four degrees almost exactly south of Sirius, and forms a triangle with it and Nu 2 Canis Majoris—all three can be seen in the same field in binoculars. The cluster itself covers an area around the size of the full moon. It contains about 100 stars including several red giants, the brightest being a spectral type K3 giant of apparent magnitude 6.3 near the cluster's center, and a number of white dwarfs. The cluster is estimated to be moving away from us at 23.3 km/s. The diameter of the cluster is between 25 and 26 light years.

Celestial pole

North Celestial Polesouth celestial polecelestial north pole
If Canopus has not yet risen, the second-magnitude Alpha Pavonis can also be used to form the triangle with Achernar and the pole. The third method is best for moonless and clear nights, as it uses two faint "clouds" in the Southern Sky. These are marked in astronomy books as the Large and Small Magellanic Clouds. These "clouds" are actually dwarf galaxies near the Milky Way. Make an equilateral triangle, the third point of which is the south celestial pole. A line from Sirius, the brightest star in the sky, through Canopus, the second-brightest, continued for the same distance lands within a couple of degrees of the pole. In other words, Canopus is halfway between Sirius and the pole.

AE Aurigae

AE AurHD 34078
AE Aurigae is a blue O-type main sequence dwarf with a mean apparent magnitude of +6.0. It is classified as an Orion type variable star and its brightness varies irregularly between magnitudes +5.78 and +6.08. It is approximately 1,300 light-years from Earth. AE Aur is a runaway star that might have been ejected during a collision of two binary star groups. This collision, which also is credited with ejecting Mu Columbae and possibly 53 Arietis, has been traced to the Trapezium cluster in the Orion Nebula two million years ago. The binary Iota Orionis may have been the other half of this collision. AE Aur is seen to light up the Flaming Star nebula, but it was not formed within it.

Principal Galaxies Catalogue

PGC 39058 is a dwarf galaxy which is located approximately 14 million light-years away in the constellation of Draco. It is relatively nearby, however it is obscured by a bright star which is in front of the galaxy. PGC 6240 (also known as White Rose Galaxy) is a large lenticular galaxy in the constellation Hydrus. It is located about 346 million light-years away from Earth. * Astronomical catalogue 49,102 morphological descriptions. 52,954 apparent major and minor axis. 67,116 apparent magnitudes. 20,046 radial velocities and. 24,361 position angles. Astronomical catalogue. PGC info at ESO's archive of astronomical catalogues. PGC readme at Centre de Données astronomiques de Strasbourg.

Wolf 359

CN Leonisstar of the same name
At a distance of approximately 7.9 light years from Earth, it has an apparent magnitude of 13.54 and can only be seen with a large telescope. Wolf 359 is one of the nearest stars to the Sun; only the Alpha Centauri system (including Proxima Centauri), Barnard's Star and the brown dwarfs Luhman 16 and WISE 0855−0714 are known to be closer. Its proximity to Earth has led to its mention in several works of fiction. Wolf 359 is one of the faintest and lowest-mass stars known. At the light-emitting layer called the photosphere, it has a temperature of about 2,800 K, which is low enough for chemical compounds to form and survive.

List of exoplanet extremes

least massive planetList of extrasolar planet extremeslowest metallicity planet-bearing star
The following are lists of extremes among the known exoplanets. The properties listed here are those for which values are known reliably.

List of nearest galaxies

closest neighborsNearest galaxiesnearest spiral galaxy
This is a list of known galaxies within 3.8 megaparsecs (12 million light-years) of the Solar System, in ascending order of distance. This encompasses all of the about 50 Local Group galaxies, and some that are members of neighboring galaxy groups, the M81 Group and the Centaurus A/M83 Group, and some that are currently not in any defined galaxy group. The list aims to reflect current knowledge: not all galaxies within the 3.8 Mpc radius have been discovered. Nearby dwarf galaxies are still being discovered, and galaxies located behind the central plane of the Milky Way are extremely difficult to discern. It is possible for any galaxy to mask another located beyond it.

Detailed logarithmic timeline

Orders of magnitude (time). Technological singularity. Timeline of evolution. Timeline of the Big Bang. Timeline of the far future. World history. Interview with Heinz von Foerster. Detailed logarithmic timeline of the Universe.

List of unusual units of measurement

football fieldfull-lengthDog year
This distance is equal to about 15.8 light-years, 149.6 Pm or 4.8 parsecs, and is about twice the distance from Earth to the star Sirius. One barn is 10 −28 square metres, about the cross-sectional area of a uranium nucleus. The name probably derives from early neutron-deflection experiments, when the uranium nucleus was described, and the phrases "big as a barn" and "hit a barn door" were used. Barn are typically used for cross sections in nuclear and particle physics. Additional units include the microbarn (or "outhouse") and the yoctobarn (or "shed"). One brass is 100 ft2 area (used in measurement of work done or to be done, such as plastering, painting, etc.).

51 Andromedae

51 And51 And (Nembus)
51 Andromedae, abbreviated 51 And and formally named Nembus, is the 5th brightest star in the northern constellation of Andromeda, very slightly dimmer than the Andromeda Galaxy also being of 4th magnitude. It is an orange K-type giant star with an apparent magnitude of +3.59 and is about 169 light-years from the Earth/solar system. It is traditionally depicted as one of the two northern, far upper ends of the mythological, chained-to-the-rocks princess, the other being binary star system Gamma Andromedae. At an estimated age of 1.7 billion years, this is an evolved red giant star with a stellar classification of K3- III CN0.5.

Lalande 21185

22 H Camelopardalisextrasolar planets
Despite this, and although relatively close by, it is (as all red dwarves) very dim, being only magnitude 7.5 in visible light and thus too dim to be seen with the unaided eye. The star is visible through a small telescope or binoculars. At approximately 8.31 ly away it is one of the nearest stars to the Solar System; only the Alpha Centauri system, Barnard's Star, and Wolf 359 and the brown dwarfs Luhman 16 and WISE 0855−0714 are known to be closer. Because of its proximity it is a frequent subject for astronomical surveys and other research and thus is known by numerous other designations.

Xi Herculis

ξ Her
The star is visible to the naked eye with an apparent visual magnitude of 3.70. Based upon an annual parallax shift of 23.84 mas as seen from Earth, it is located 137 light years from the Sun. At that distance, the visual magnitude of the star is diminished by an extinction factor of 0.05 due to interstellar dust. It is a suspected member of the Sirius stream of co-moving stars. This is an evolved G-type giant star with a stellar classification of G8 III. It is a red clump star, which means it is on the horizontal branch and generating energy through the thermonuclear fusion of hydrogen at its core. The star is emitting X-rays with a luminosity of 3.03e30 erg s −1 in the 0.3–10 keV band.


κ OriKappa Orionisκ Ori (Saiph)
Parallax measurements yield an estimated distance of 650 light-years (198 parsecs) from the Sun, which is about the same as Betelgeuse. It is smaller, less luminous but hotter at its surface than Rigel with an apparent visual magnitude of 2.1. The luminosity of this star changes slightly, varying by 0.04 magnitudes. Kappa Orionis is the star's Bayer designation and 53 Orionis its Flamsteed designation. The traditional name Saiph is from the Arabic saif al jabbar, 'سیف الجبّار' literally sword of the giant. This name was originally applied to Eta Orionis.

Timeline of white dwarfs, neutron stars, and supernovae

in Serpens is observed. 1862 – Alvan Graham Clark observes Sirius B. 1866 – William Huggins studies the spectrum of a nova and discovers that it is surrounded by a cloud of hydrogen. 1885 – A supernova, S Andromedae, is observed in the Andromeda Galaxy leading to recognition of supernovae as a distinct class of novae. 1910 – the spectrum of 40 Eridani B is observed, making it the first confirmed white dwarf. 1914 – Walter Sydney Adams determines an incredibly high density for Sirius B. 1926 – Ralph Fowler uses Fermi–Dirac statistics to explain white dwarf stars. 1930 – Subrahmanyan Chandrasekhar discovers the white dwarf maximum mass limit. 1933 – Fritz Zwicky and Walter Baade propose the neutron

NGC 4565

Needle Galaxy4565
NGC 4565 (also known as the Needle Galaxy or Caldwell 38) is an edge-on spiral galaxy about 30 to 50 million light-years away in the constellation Coma Berenices. It lies close to the North Galactic Pole and has a visual magnitude of approximately 10. It is known as the Needle Galaxy for its narrow profile. First recorded in 1785 by William Herschel, it is a prominent example of an edge-on spiral galaxy. NGC 4565 is a giant spiral galaxy more luminous than the Andromeda Galaxy. Much speculation exists in literature as to the nature of the central bulge.

Known Space

ARMJinxtransfer booth
It orbits Lambda Serpentis (27 Serpentis), a G0 star 34.7 light-years from Earth. It is named after its discoverer, J. Margrave Julland. Silvereyes is, at the time of Ringworld, the furthest Human world from Earth (21.3 light-years, 60 days at Quantum-I hyperdrive speeds), orbiting Beta Hydri. In Niven's obscure story The Color of Sunfire it has entire continents covered with Slaver sunflowers (bred as defense for Thrint manors, they focus sunlight using silver leaves as parabolic reflectors), giving it an appearance from orbit of having "silver eyes".

Timeline of stellar astronomy

Suvi Gezari's team in Johns Hopkins University, using the Hawaiian telescope Pan-STARRS 1, publish images of a supermassive black hole 2.7 million light-years away swallowing a red giant.

HD 220105

HD 220105 is a star in the northern constellation of Andromeda, and a member of the Sirius supercluster. It lies near the lower limit of visibility to the naked eye at an apparent visual magnitude of 6.24, and can be a challenge to spot under normal viewing conditions. The star is located 239 light years away, based upon an annual parallax shift of 13.63 mas. It is moving closer to the Earth with a heliocentric radial velocity of −2 km/s. This is an A-type main-sequence star with a stellar classification of A5 Vn, where the 'n' notation indicates "nebulous" absorption lines due to rapid rotation. It is around 525 million years old with a high projected rotational velocity of 259 km/s.


In 964, the Andromeda Galaxy, the largest galaxy in the Local Group, was described by the Persian Muslim astronomer Abd al-Rahman al-Sufi in his Book of Fixed Stars. The SN 1006 supernova, the brightest apparent magnitude stellar event in recorded history, was observed by the Egyptian Arabic astronomer Ali ibn Ridwan and Chinese astronomers in 1006. Some of the prominent Islamic (mostly Persian and Arab) astronomers who made significant contributions to the science include Al-Battani, Thebit, Abd al-Rahman al-Sufi, Biruni, Abū Ishāq Ibrāhīm al-Zarqālī, Al-Birjandi, and the astronomers of the Maragheh and Samarkand observatories.

Nu2 Canis Majoris

ν 2 CMa7 Canis MajorisNu 2
With an apparent visual magnitude of 3.96, it is bright enough to be seen with the naked eye to the southwest of Sirius. It has an annual parallax shift of around 50.63 mas as seen from Earth, thus this system is about 64.4 light years from the Sun, a parallax well within the error margins of the figure later given by the Gaia space observatory data release 2, namely 50.471 ± 0.4168. It is an evolved K-type giant around 4.6 billion years old. Around 1.3 times as massive as the Sun, it has expanded to around 4.9 times the Sun's diameter and 11 times its luminosity. In 2011, it was found to have a planet.

NGC 7418

Galaxies like the Milky Way and the Andromeda Galaxy have been found to host both. The stellar population at the nucleus of NGC 7418 has been found to be quite young, with mean age less than 100 million years, indicating recent star forming activity. One supernova has been observed in NGC 7418, SN 1983 Z. It was discovered by L. E. Gonzalez at Cerro El Roble 11" west and 52" south of the nucleus. On September 3, 1983 it had an apparent magnitude of 15.5. NGC 7418 is a member of a galaxy group known as the IC 1459 group. It is a loose group centred at IC 1459 and contains a large number of spiral galaxies.

28 Cygni

28 Cygb 2 Cygnib 2 Cyg
It is a faint blue-white hued star but visible to the naked eye with an apparent visual magnitude of 4.93. The distance to 28 Cyg, as estimated from its annual parallax shift of 5.3 mas, is around 620 light years. It has an absolute magnitude of −2.56, which means that if the star were just 10 pc away it would be brighter than Sirius, the brightest star in the night sky. This is a B-type main-sequence star with a stellar classification of B2.5 V, per Lesh (1968). Slettebak (1982) found a class of B2 IV(e), which would suggest this is a more evolved subgiant star. It is a Be star, which means the spectrum displays emission lines due a disk of ejected gas in a Keplerian orbit around the star.